1. Field of the Invention.
The present invention relates generally to electrical conductivity liquid sensing devices, and more particularly, to such sensing devices that are designed to prevent the false indication of the presence of liquid.
2. Background of the Invention.
Many strategies are known for sensing the presence or absence of liquid in a container. In particular, various sensors are known that use a pair of electrically conductive probes that extend into the container, wherein the liquid provides for conductivity between the probes. Thus, if a potential is applied across the probes and a current flow is sensed, the presence of liquid in the container is indicated. Conversely, when current no longer flows between the probes, that is an indication that the container is empty.
However, prior art sensors of this type experience difficulties if the liquid being sensed has any tendency to foam, such as is the case with cleaning solutions, and the like. The difficulty arises wherein such prior art probes are not able to differentiate between the liquid itself and the foam it produces. Thus, foam can indicate the presence of liquid when, in fact, the container is empty.
Further problems with such electrically conductive probes arise when the liquid forms an electrically conductive bridge from one probe to another, falsely indicating the presence of liquid. Such bridging typically occurs at the proximal end of the probe adjacent the top of the container. In this situation, the liquid contacts a proximal end or cap surface, and flows there along between the probes. This form of bridging has been found to be very persistent, especially in the enclosed environment of a container wherein the bridging liquid does not readily dissipate or dry out. Moreover, it has been found that conductivity occurs even after the drying out of the liquid, as the residue left behind can often times be sufficiently conductive.
Accordingly, it would be very desirable to have an electrical conductivity liquid sensing probe that is not susceptible to false readings as a result of liquid foaming, and prevents the forming of electrically conductive bridges between the probes.